The present invention relates to a novel, advantageous process for the preparation of 3-isochromanones by cyclization of o-chloromethylphenylacetic acids. Isochroman-3-one is of great interest as an intermediate in the synthesis of pharmaceuticals and plant protection agents.
WO 97/12864 discloses, for example, the use of 3-isochromanone as an intermediate in the preparation of fungicides and pesticides and WO 97/48692 discloses the use of 3-isochromanone in the preparation of certain agricultural products.
3-Isochromanone is a known compound and a large number of methods for preparation are mentioned in WO 97/48692. For example, 3-isochromanone can be prepared by Baeyer-Villiger oxidation of 2-indanone using hydrogen peroxide in sulfuric acid and acetic anhydride or using m-chloroperbenzoic acid in combination with trifluoroacetic acid or by reaction of bromomethylphenylacetic acid with KOH in ethanol with ring-closure.
WO 97/48692 discloses a synthesis of 3-isochromanone by chlorination of o-methylphenylacetic acid with sulfuryl chloride in the presence of free radical initiators and by subsequent reaction of the resulting 2-chloromethylphenylacetic acid with a base. The disadvantage of this process is the formation of one equivalent of salt per equivalent of 3-isochromanone in the reaction of 2-chloromethylphenylacetic acid using a base and the handling of reaction mixtures containing salts.